Synthesis of homo-metallic heavier analogues of cyclobutene and the cyclobutadiene dianion

The reduction of the boryl-substituted SnII bromide {(HCDippN)2B}Sn(IPrMe)Br with 1.5 equivalents of potassium graphite leads to the generation of the cyclic tetratin tetraboryl system K2[Sn4{B(NDippCH)2}4], a homo-metallic heavier analogue of the cyclobutadiene dianion. This system is non-aromatic as determined by Nucleus Independent Chemical Shift Calculations (NICS(0) = −0.28, NICS(1) = −3.17), with the primary contributing resonance structures shown by Natural Resonance Theory (NRT) to involve a Sn=Sn double bond and 1,2-localized negative charges. Abstraction of the K+ cations or oxidation lead to contraction or cleavage of the Sn4 unit, respectively, while protonation generates the neutral dihydride cis-1,2-Sn4{B(NDippCH)2}4H2 (a heavier homologue of cyclobutene) in a manner consistent with the predicted charge distribution in the [Sn4{B(NDippCH)2}4]2- dianion.